This is my first tutorial fully written on english, then I beg your pardon for any sintax error or mistake I made have — thanks!.
In the following link you have a FEMAP & NX NASTRAN Tutorial explained step-by-step dealing with Thermal Coupling of Steady-State Heat Transfer Finite Element Analysis from CHIP to PCB (Printed Circuit Board) with GLUE Surface-to-Surface Thermal Contact and Orthotropic Material Properties:
I have created in FEMAP the following picture that explains the problem very well:
The loads & boundary conditions are the following:
- A heat load Q= 5 Watt applied to the top surface of the chip.
- A temperature constraint of 25°C applied to the edge of the PCB opposite to the edge closest to the chip.
- A convection coefficient applied on the top and side faces of the chip of 24 W/m2ºC.
- A convection constraint to the top face of the PCB with a heat transfer coefficient = 19 W/m2ºC, being 25ºC the ambient temperature of the fluid around the PCB.
- A thermal coupling between the CHIP & PCB, assuming the chip is connected to the PCB using a Ball Grid Array (BGA) solder connection with a total area that is half of that of the chip.
- Assume as well a Pb-Sn weld of thermal conductivity Ksolder= 80 W/mºC and a gap of 1 mm. We can then calculate the total conductance as follows:
Heat Transfer Coefficient =
ksolder * Asolder / (Lgap * Achip) =
80*0.5/0.001*1 = 40e3 W/m2ºC
For simplicity, I suggest to use always GLUETYPE=1 and PENTYP=2, which allows you to directly specify the conductance via PENN, having the following units:
Thermal Conductivity in SI has units of W/mºC, thus PENN has units of W/m2ºC, then we can use directly the value of Heat Transfer Coefficient for the Thermal Coupling.
The PENN value is independant of the GLUE surface area, the user does not need to know the glue surface area by advance, this value is computed by the glue algorithm and is a function of the mesh size & shape, glue refinement, etc..
So, setting “Glue Type = 1..Spring“ (GLUETYPE=1), also “Penalty Factor Units = 2…Force/(Length x Area)“ (PENTYP=2) and “Normal Factor = 0.04” W/mm2ºC (PENN), the definition of GLUE Thermal Coupling parameters will be correct as shows the following image:
The following picture shows the final steady-state results of temperature distribution in the Chip & PCB components where you can see the effects of the orthotropic material in the temperature distribution: Heat is better conducted in the Y orthotropic material direction. Temperatures vary from approximately 25ºC to 60ºC.
The following picture shows the temperature gradient in the chip, with the values on the color bar limited to those found in the Chip only by means of using Groups:
I hope the above tutorial to be helpful & useful.